1. Field of the Invention
The present invention relates to a coil assembly (often called simply “coil) for a rotating electric machine, to a rotating electric machine employing the same, and to a manufacturing method for these. In particular, the present invention relates to a coil assembly for an axial gap rotating electric machine, to a rotating electric machine employing the same, and to a manufacturing method for these.
2. Description of the Related Art
Rotating electric machines of axial type (electric motors and electric generators) equipped with a disk-shaped rotating armature coil are known in the art to date. Since rotating electric machines of axial type can be made shorter in length in the axial direction than radial gap rotating electric machines, they enjoy wide-spread use in applications in which axial length must be kept to a minimum, as, for example, in audio equipment, video recorders, computer disk drives, automotive radiator fans, window lifts, and the like.
One type of coil used in conventional rotating electric machines of axial type is a disk-shaped coil composed of a plate of conductive material (copper or aluminum) that has been formed into a coil pattern by pressing or other process, and the coil pattern then affixed to an insulating sheet or similar material and connected to a different coil pattern by soldering or welding. Prior art examples of such disk-shaped coils are disclosed in U.S. Pat. No. 3,090,880, U.S. Pat. No. 3,189,770 and U.S. Pat. No. 3,144,574.
Another known type of coil used in axial rotating electric machines is a disk-shaped coil produced by a process of arranging, in the circumferential direction, a required number of formed coil units of wound magnet wire.
Prior art publications relating to coils for rotating electric machines and related technologies include ten patent publications, specifically, U.S. Pat. Nos. 3,090,880, 3,189,770, 3,144,574, 3,944,857, and 6,411,002; Japanese Patent Laid-Open Publication 59-165935; U.S. Pat. No. 3,488,539; Japanese Patent Post-Exam Publication 48-442; and U.S. Pat. Nos. 3,790,835 and 5,744,896.
The disk-shaped coils disclosed in U.S. Pat. Nos. 3,090,880, 3,189,770, and 3,144,574 are fabricated through the application of printed circuit board production technology; since the coil pattern affixed onto the insulating board is extremely thin, there are necessarily limitations as to the amount of current that can flow through the coil. For this reason, the coils disclosed in U.S. Pat. Nos. 3,090,880, 3,189,770, and 3,144,574 are limited to application in rotating electric machines having low output on the order of several hundred watts to several kilowatts.
To make a coil for a rotating electric machine adapted for high output/high torque applications, it is necessary to increase the cross-sectional area of the coil to boost its electric current capacity. A known method for enabling this, as disclosed in Japanese Patent Laid-Open Publication 59-165935, U.S. Pat. No. 3,488,539, and Japanese Patent Post-Exam Publication 48-442, is to stack printed circuit boards in multiple stages and electrically connect the different coil patterns to each other via through-holes or the like. Such coils become thicker in relative terms and acquire higher electric current capacity as the number of stages increases in the printed circuit boards, but since the insulated parts of the printed circuit boards will also have a multistage design at the same time, the magnetic gap will increase, possibly causing a drop in magnetic flux level or a drop in output of the rotating electric machine.
Also known in the art is a coil of the type disclosed in U.S. Pat. No. 3,488,539 and Japanese Examined Patent Application 48-442, composed of two layers which are bar-shaped half-coil conductors that are shaped to the necessary cross-sectional area by bending, punching, or other mechanical working process, and provided with an insulating board disposed between them. The ends of the two half-coil conductor layers form a disk-shaped coil by being joined by welding or the like, so as to form a coil loop. However, in a coil of this type, if the conductor width of the half-coils perpendicular to the magnetic flux is reduced and the number of conductors is increased with the object of reducing eddy current or boosting voltage, the half-coil conductors will have lower rigidity, making it difficult to machine the half-coil conductor pattern with a high degree of accuracy, or to position the two half-coil layers when connecting them. Additionally, smaller width in the half-coil connecting portions and the increased number of connecting portions will result in a more difficult welding or other joining process.
According to the designs disclosed in U.S. Pat. Nos. 3,790,835 and 5,744,896, the two straight sides of a coil unit, which are effective for torque, are positioned mutually adjacent to the two sides of the other coil unit while keeping the thickness in the coil section facing the magnets less than that in the coil end connecting portion, thus reducing the drop in magnetic flux level caused by the increased magnetic air gap. With this design, since the coil end connecting portion where the coil units overlap is positioned outside the zone facing the magnets, it will be necessary for the coil end connecting portion to project out in excess beyond the inner and outer peripheral sides of the face which faces the magnets. As a result, the coil loop will have a longer path length, and the resistance of the coil will be higher.
Arrangements for reducing the diametrical length of the coil end connecting portion include bending up the coil end connecting portion, or forming the portion to desired shape together with the coil end connecting portion of the other coil unit. However, since the coil units are composed of a number of bundled wires, if a forming process such as that mentioned above is performed, the wire diameter for a serviceable coil unit will be limited. Specifically, if wire diameter is increased to accommodate larger current, it will be more difficult to bend or form the coil end connecting portion, whereas, conversely, if there is adopted a design in which a larger number of finer wires is bundled and connected in parallel to provide the necessary current path cross sectional area, it will be necessary to electrically connect the individual wires, and the reliability of the electrical connections will be lower as the number of wires increases. Moreover, commonly used magnet wires are round and difficult to wind in alignment, and thus the arrangements disclosed in U.S. Pat. Nos. 3,790,835 and 5,744,896 will have a lower conductor fill factor in the coil.
In particular, in cases in which a coil is used in a slotless, coreless, or similar arrangement, the space occupied by the coil will be within the air gap of the magnetic circuit, and a greater coil thickness will mean a larger air gap and a consequent possible drop in magnetic flux level, leading to a lower output and torque of the rotating electric machine. In order to prevent such a drop in output and torque, it will be necessary to increase the magnetic flux level within the air gap, but if magnet usage is increased with the aim of increasing magnetic flux, the rotating electric machine will be bulkier, heavier, and more expensive to manufacture.
With the foregoing in view, there exists a need for a coil for a rotating electric machine which is endowed with a high conductor lamination factor and dimensional accuracy, and which is moreover simple to manufacture and is capable of service at high current; for a method of manufacturing the same; for a rotating electric machine; and for a method of manufacturing the same.